To achieve good noise performance of a radio receiver, e.g. used for cellular communication in a mobile terminal or base station, it is desirable to have a low-noise amplifier (LNA) with high gain and low noise. This enables reception of very weak signals. A further demand on the LNA is sufficient linearity to be able to handle interfering signals, and it is also desirable that good input power match is provided that is a well defined resistive input impedance to ensure proper operation of preceding elements such as band select or duplex filter.
To provide input power match and simultaneously achieve the low-noise properties, inductive series degeneration has been used. An example of an amplifier using this is illustrated in FIG. 10. A drawback of this solution, in addition to its inflexibility in design, is the large area occupied by on-chip inductors, or the alternative demand of expensive and volume consuming external inductors. Further examples according to this principle are disclosed in US 2006/0284670.
Another approach is to use a common-gate LNA, which enables wider bandwidth operation and less inductors compared to the approach described with reference to FIG. 10. An example of this approach is illustrated in FIG. 11. The approach is further described in Zhuo et al., “A Capacitor Cross-Coupled Common-Gate Low-Noise-Amplifier”, IEEE Trans. on Circuits and Systems, Vol 52, No. 12, 2005. However, the nature of a common-gate LNA is that the low-noise properties of the inductively degenerated approach described with reference to FIG. 10 cannot be achieved. The common-gate LNA is therefore not considered a suitable choice for demanding implementations, such as use in mobile terminals where both low-noise properties and low power consumption are required.
It is therefore a desire to provide an amplifier suitable for such demanding implementations.